Basic refractory brick and process



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R. P. HEUER BASIC REFRACTORY BRICK AND PROCESS Filed Dec. 51, 1949 lROME) Ml X E R MOLD auras DR Y COARSE PARTICLES 5 2'0 70,8v

OH CH May 26, 1953 IRON POWE (3 r0 /5z) INV RUSSELL PEARCE ATTORNEYS Patented May 26, 1953 25,639,993, BASIEREFRAC'EORY nnrclr -annvrnocuss Russell Pearce Hcuer, .Villanova... Pa assignor. to General Refractories Company, a. corporation.

or Pennsylvania Application Decemherfil, 1949;;SeriaL-No. 11363354 nesite) orelectrically fused magnesia, and which are suitablefor usewithout kiln firing,

.A purpose of the invention is to obtain. an improved. strength .or, modulus of rupture at intermediatetemperatures innnfired basic refractory brick.

A. furtherpurpcse isto avoid or minimizethe shrinkage which may occur in the linear dimensions. of unfiredi basic .refractorybr-ick-When they are heated. to high temperatures.

A further purpose isto use 45 to .70-peroent (preferably 50 to 60 percent) of coarse magnesia particles between 6. and. 35.. mesh andpreferably between 8 (and .35.mesh, from.25 to 50.percent of fine, magnesia particles whichpassthrough 48 mesh, and, preferably through. 65- mesh; and. from 3 to 215,.percent,preferably 8 to 12 percent, of liner particles. of metallic iron which-pass through a.28..mesh per linear inch screen and preferably pass through. 2....35. mesh per linear inch screen,

with a suitable bonding agent such assulphuric acid .or. magnesium sulphate and water, to form the. mix into brick under suitable. molding pressure and to cure andrdry orclry-thebrich without, kiln firing.

Aiurther purpose is to replace the coarse magnesia particles either partially or entirely :by coarsechromite particles which are oig-a size between .6. and. 28 mesh per linear inch.

A further. purposeis to cure the molded. brick with carbon. dioxide gasto improve the low tem-- perature. strength of the brick.

Further'purposesappear in the specification and. in theclaims.

Inthe (lrawingsdiigure 1 is a chart showing the stepsinthe. process. I

Figure 2- is a diagrammatic view of apparatus for curing of the-brick Withcarbondioxide.

In my.U..S..Patent.No. 1559 512 I describea magnesia refractory suitable for use. Withoutk'iln firing WhiChiShbOl'lded withabout percent. of

claynand sodium acid sulphate. My U.,S-. Patent No; 1,992,482 describes. a. similar composition.

In producing the magnesia refractories of my patents just inentioneil have found that unfired. refractories. thus made-and: exposed to furnac temperature. during use suffer-a substantial loss in strength at intermediate temperatures suchas 800 C. .to 1200" C. Thisis; due to the fact that-the bond-which is. formed during the curing or drying of the brick comprises magnesia .2, compounds containingwvater and -vc1atile-. c0m.- ponents; Uponheatingto elevated temperatures, these compounds-are destroyed andzthe strength of the brick. is lowered substantially- When.- th brick-is heatedto a; temperature of-L500P C-.. new ceramic bonds-are formed which ofisetthe loss. of the low temperature bonds. However even While the iurnaeei is--operating at 1-500, C. a sub stantial thermal .gradienhprevails inthe brick 1 walls,.so.that-, a, portion oirthebriclralew inches back froma hot-face:maintained-at 150.0 C-.. may be heated. to aitemperataireintherange ,from 800 to, 120.0 G and may never reach" a tempera- .tureof .1500" This pmfloftherbrickwhich operates at intermediate temperatures: may therefore. :sufier from -l-ack of strength.

Very. .considerable stresses are .develeped the. brick. during...eperatio-n orthea furnace, anti as a result of thesestresses cracks maydevelop. behind the hot face which will realise the -hot face to break off. This character of failure has been freq uentlyencounteredr iltiis thusyery important to .dBVGlQpa-fifl. increased strength at intermediate temperatures in basic'refractory brick.

vI have discoveredthat by incorporation in the refractory .mixnf from. 3- tolfijpercent of metallic ironpowder which: is fineenoughin particle size to, passthrough a. 28 mesh per linear inch: screen 30 and preferably througha .35 mesh per linear inch screen) muchof the vdifficulty.abovereferred to can b ,overcome. ,Ipmfer to use areiractorymixofhcoarse. aniline magnesia, particles the .coarse particles. constituting from -to leper-- cent (preferably. 50. to. (SO percent) of the;- total mix landcbeing sized to pass-through a. 6- mesh per linear inch screen and preferably through an 8.. meshper linearlinchrscreenand vto rest upon e135 meshper linear-inch-screen. I. likewise prefer to. employ from 25 to percent of fine magnesia particleswhich pass through; 9,48 mesh per linearinchscreen and preferably through a 65.mesh.;per, linear inchscreen. Fine chromite of the sameisize may. be substituted for .finemagnesia, but: for best resultsthe amquntof chromite finer than 35, meshper linear .inchshould. be kept to a minimum, although formany. purposes .upto ten percent, of. fine chromite; may. .be employed. .From 3 to"15 percent andpreferably. from 8 to 12percent .of...iron pQWdBI,--iS 1lS8d.;in the mix, WllCh completes the refractory compositionexcept. for theibond in them-preferred, embodiment.

In. making. iupthe; refractory it is'preferable ,to..firstemixthacoarseesnd fine. refractory p rticles together in a wet pan or other suitable mixer and then moisten them with the binder solution. The binder may be sulphuric acid in the proportion of 0.5 to 3 percent on the Weight of the total dry refractory components of the mix, along with 2 to percent of water on the Weight of the total dry refractory components, preferably about 1 percent of acid and 4 percent of water.

Where magnesium sulphate is used instead of sulphuric acid, I preferably use 0.5 to 3 percent of anhydrous magnesium sulphate on the weight of the total dry refractory components, with 2 to 5 percent of water on the total dry refractory components, preferably 1.3 percent of anhydrous magnesium sulphate with 4 percent of water.

In the case of sulphuric acid as a binder it is important to mix the sulphuric acid with the refractory and allow it to react before the iron powder is added, and then continue mixing to incorporate the iron powder. Where magnesium sulphate solution is used as a binder, however, this order of mixing is not important.

The mix containing the coarse and fine refractory particles, the iron powder, the binder and the water, is molded into the desired refractory shape after the mixing is complete, desirably proceeding with sufiicient promptness so that the iron powder does not become heavily oxidized prior to molding. The molding can be accomplished in hydraulic or mechanical presses as well known in the art, using pressures in excess of 1,000 p. s. i., preferably more than 5,000 p. s. i. and still better in excess of 10,000 p. s. i. applied to the brick surface. Jolting, impacting or other molding means may be used as an alternative to the forming press.

After molding, the brick may if desired be directly dried, preferably employing drying temperatures up to 150 C. The brick are then ready for use without kiln firing. Figure 1 illustrates in chart form the sequence of steps in making the brick.

As an alternate to the direct drying of the molded brick, the brick may desirably be cured with carbon dioxide gas before the drying. Where curing is to be employed, the molded brick as they are formed are placed in a suitable gas tight chamber which is evacuated and then filled with carbon dioxide gas, preferably at a gage pressure of about 15 p. s. i. Higherpressures may be used up to any desired pressure, but are not necessary. The exposure to carbon dioxide gas is maintained for at least one hour and preferably about six hours or longer at room temperature whereupon the brick are removed from the treating chamber and dried, suitably at temperatures up to 150 C. for times as long as 35 hours.

The technique used in curing may follow that of my copending application Ser. No. 756,001, filed June 20, 1947, for Unburned Refractory Brick Making, now Patent No. 2,547,323, April 3, 1951. As shown in Figure 2, a treating chamber of steel or the like has a bottom track II to receive cars l2 through a suitably sealed door I3. The chamber is capable of withstandin a vacuum of 29 inches of mercury and a pressure of at least 1 atmosphere. A source of carbon dioxide gas is provided at M connected to the treating chamber by a pipe l5 through a valve IS. The source may be Dry Ice heated by a steam coil [1.

The treating chamber II] is provided with a vacuum pump l8 connected to the treating chamher on the inlet side of the pump by a pipe I! controlled by a valve 20. On its discharge side, the vacuum pump may either waste gas through pipe 2| controlled by valve 22 or may supply it through pipe 23 controlled by valve 24 to the inlet side of a gas compressor 25 which feeds through a pipe 26 to a storage tank 27, connected to the treating chamber by a pipe 28 controlled by a valve 29.

When a charge enters the curing chamber, the chamber is first evacuated, wasting the air passing through the vacuum pump, and then carbon dioxide is introduced from the storage and additional carbon dioxide is provided from the generator. The treating gas need not be pure, but may contain nitrogen or oxygen, which are effectively inert, in addition to carbon dioxide.

The pick up of carbon dioxide in the brick as a result of the curing treatment is in the range between 0.25 and 2.5 percent, preferably 1 percent on the total weight of the dry refractory components of the brick.

Brick made in accordance with the above procedure have a modulus of rupture at room temperature of 1500 p. s. i. or more.

When the brick of the present invention are heated to 1200 C., the strength at this intermediate temperature is much higher than that of ordinary brick. While the brick according to my U. S. Patents Nos. 1,859,512 and 1,992,482 have a modulus of rupture at 1200 C. of only about 250 p. s. i., typical brick made according to the present invention have a modulus of rupture at 1200 C of 750 p. s. i. and many run even as high as 1200 p. s. i. The brick according to the present invention have a modulus of rupture at 800 C. which is even higher than that at 1200 C.

While the greatly improved strengths at intermediate temperature are important characteristics of the brick of the invention, the negligably small shrinkage in volume on heating to 1650 C. and cooling to room temperature is an equally important feature of the invention. Prior art unfired magnesia brick on heating to 1650 C. and cooling to room temperature have exhibited a volume shrinkage of at least 15 percent, whereas the brick of the invention in most cases shrink only about 1 percent and. in any case have a volume shrinkage less than 2 percent. The low shrinkage results in minimizing shrinkage cracking and avoiding the corresponding loss which occurs.

The very desirable properties of low shrinkage and high strength at intermediate temperatures are caused by the action of the metallic iron powder present in the mix. This finel divided metallic iron is in contact with the particles of magnesia in the refractory. When the brick is dried (or dried and cured) at low temperature bond is developed by the magnesia particles reacting with magnesium sulphate and moisture present in the brick mix. But when the brick are heated to intermediate temperatures, these magnesia bonding compounds are broken down with the loss of their volatile components. In this manner much of the strength of the brick derived from this source is lost. However, when temperatures are reached in the intermediate range between 800 C. and 1200 C., the finely divided iron powder begins to oxidize. The oxidation may continue until the iron forms ferric oxide. The iron oxide, usually ferric oxide, reacts with the magnesia to form a bond which is believed to be magnesium ferrite, MgQFezOs. To produce magnesium ferrite a.

masnesiaparticlss anditheisimilltaneous eigmmr- 10.;

on produc awcnystallin bond-which;r nts-to bridge. the; mirlispaces which-form -.batween.-the indivi.dua1...magncsia partioleslwhentathe volatile mponents-of the zori inal'bomz inesubstances are driven off-f In zthisawayi Lnewt bondeisicte 115 ated. which is crystallinoiand"rhighlx refraeto Thisrnewibond usemu hisun rior,t rthe clett hand; of the S. patents-abo e cfierreditocasedem- OILStIEitBd-HN[the high-. mQdu1HS' ofo-nupturer 60.. ne ent; @6203 about. 14 percent. H I

fI-hairon. powder emp oye ma e mmerc sponge iron powder. whi h: isavailahle i 6 us 14:.v percent; qMa about.

,in. the lso calledpowder metallurgy process in;

which ,;meta 11ic- .,objectsv .aneformed :b y. pressing metallic powden under high pressure and sintering. This is, essentially iron-with small: amounts of;,;irnpurities. other .compositionof iron powder. may be used-suchas.: that obtained b reducingoxides 10f x-ironsuchas milliscale with gaseous reducing agents; jI'he-iron-powder may alsowbe rmade Joy tgrinding cornmerciai. cast iron. Produots ofmachiningymay also be :used, where thei size-is adequately fine,,ls,uchi as., p1ain carbon steel; orvausteniticaor ferriticstainless steel.

,Ilypicalr examples of the; compositions of the invention embodying the principles :above et forth areashQWn bythe -fol1owing=tab1ez Example Nb'nn; 3 4 5 -6 =7 8 9 -10 "11 12 13 14 15 -16 Reiractorycomponents: 1 I l 3 floarsemaimcsia 8.x 351uesh,-;percenti 55 62 5O Coarse chromite, 6 8 mesh pcrcent i 'Fine-magnesiathrougthkfir mesh; percent. .45 :25. :35 '35 35 ,F inachromite through-48 rocsh peroent i L "lron powder through 28gnesh pcrcent i. i 10 5 5 10' l5 BondandtGure: i 2 i j Sulphuticacidrnpcmo t v1 1 1,

Magnesium sulphate, percent i(lartionfdioxide pcroe ti i L I amaware ofpropqsals by othezgsthat retractoryiproductsbe madejtfromiay mixture ofichrome ore,'peric1'ase and iron oxide. Iron OXidG'WhBIl employed in the manufacture of magnesia-bearing refractories causes shrinkage ofht-h'e magnesia. I"haveused iron oxide in the'production of magnesia-bearing refractories, and have found that it is very inferiorto-metailic ironpartioles both in bonding and" in eliminat ig shrin age at high temperature inmagnesia reiracto.- ries. Whereas iron oxijdehas-Iio ability expand; iron particles are potentially expanding.

Wherehigh-temperature service to "be encountered. it is preif'erred'to ,useelectri'caliy fused magnesia in making my refractory. "iiorljower temperature service Iobtaindesirable results with perioiase manufactured hy' precipitating magnesiurn hydroxide from brine or sea -water.,and calcining the hydroxide .withadditionsito storm a dense rained product orahulksn cifi eravit of. aiaoutfiilo. .I. also may. us e.-.dead-bu1%ncd mag.- nesite. obtainedv by w, calcining, natural magnesium.

carbonate.

Atypical range oi anaixsis fonrefracto-iyyrmag nesi-a. suitable for iiithewpresent inver tion The chromite usedmayhave-a typical analysis as 'follo ws, which is-representative of any good refractory chromite: S102, trace to 4} percent; Cr2s,"-30 to Eo -percent; 'Grzo'rpl-us M203about Allmesh given are in {Ifyler standard mah per linear'inch.

All pe e tage giv n. he ein ene c nta cs y weighton the-total dryreiractory components, ce op r n aa .Qf shr nkage- .T c magnesia, chromite (Ham and ironmake up the total dry refractory components, and total p c n e perce ta e o bo d of" wat r a d of carbon dioxide are not included in the dry refractory components lout are basedon the total' thereof.

The rick of heprese tinv ntionares i abl for. us ight m e atur serviqesu hastwalls andr ofsofibasi .Qncnihearthsteeliurnace and Q pe r venbatoryfurnaccswi hqu .nr iou firing.

In ,view. o inventiona i d s lo ure. va iations and modifications to rneet individua1.,,whim r pa i nlar ne d will d ubtl s becom eviden to others skilled in the art, to obtain all orpart of the benefits of my inventifln withoutwcopyinc the stru tur and moqessshown .a dl, t e

r v l m a lsuc n ofa a thc ifallwith n t reasona l spiri an sc pe. ,of, my claim Havin thu described an invention what claim asneW, a d desiret se ure.byiLetterstBatent is;

1. Ahasi r fractorxbri lii unfire and suitable for .use unfl edi c rnditionkcom risin .n from A to 'ZO-DBIQfiflt; oicoalt cr. r iractcr par i f the.

lass cnsistinsof masn sial p rticl s. betwee 6 and me h and c romite.- particl b we n and, 2,8 mesh, ifrom. 2.5.. ton- .50 percent of finer refractox .nar i le t u h a mes o the classnsist n inf mag e ia r icle an chr mit particles and, from}. to, ,15 percent of ironparticles through 28 mesh. I

2-. EA basi rref'ract r :br ck, xti ifused and u ta l tor usai unfire onditi icom rising r m.

50 v.t.o...6 percen f; coarse r fra tory part cles of l.-as. c nsis ina of-ma n si particl s be w e 8 n 3 411 5.11 andchrom t particles betwee 6 .d;2B..mesh r m 3.0 t fw ne iqentu f. lin r i actory aarticics .1PIJ IQL El iG HmQSh. of ztime.class consisting of magnesia particles and chromite particles, and from 8 to 12 percent of iron particles through 35 mesh.

3. A basic refractory brick, unfired and suitable for use in unfired condition, comprising from 45 to 70 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from 25 to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and chromite particles, from 3 to 15 percent of iron particles through 28 mesh and a binder.

4. A basic refractory brick, unfired and suitable for use in unfired condition, comprising from 45 to 70 percentof coarser refractory particles of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from 25 to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particlesand chromite particles, from 3 to 15 percent of iron particles through 28 mesh and from 0.5 to 3 percent of sulphuric acid on the total of the dry refractory components.

5. A basic refractory brick, unfired and suitable for use in unfired condition, comprising from 45 to 70 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from 25 to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and a mixture of magnesia particles and chromite particles to the extent of not more than percent of the brick, from 3 to percent of iron particles through 28 mesh and from 0.5 to 3 percent of magnesium sulphate on the total of the dry refractory components.

6. A basic refractory brick, unfired and suitable for use in unfired condition, comprising from 45 to 70 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and a mixture of magnesia particles and chromite particles to the extent of not more than 10 percent of the brick, from 3 to 15 percent of iron particles through 28 mesh, a binder and from 0.25 to 2.5 percent of carbon dioxide on the total of the dry refractory components.

7. A basic refractory brick, unfired and suitable for use in unfired condition, comprising from 45 to 70 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and mesh and chromite particles between 6 and 28 mesh, from 25 to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and a mixture of magnesia particles and chromite particles to the extent of not more than 10 percent of the brick, from 3 to '15 percent of iron particles through 28 mesh, from 0.5 to 3 percent of sulphuric acid on the total of the dry refractory components and from 0.25 to 2.5 percent of carbon dioxide on the total of the dry refractory components.

8. A basic refractory brick, unfired and suitable for use in unfired condition, comprising from to 70 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from 25 to percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and a mixtureof magnesia particles and chromite particles to the extent of not more than 10 percent of the brick, from 3 to 15 percent of iron particles through 28 mesh, from 0.5 to 3 percent of magnesium sulphate on the total of the dry refractory components and from 0.25 to 2.5 percent of carbon dioxide on the total of the dry refractory components.

9. The process of making an unfired basic refractory brick which is of increased strength at intermediate temperaturewhich comprises mixing from 45 to '70 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from 25 to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and chromite particles and from 3 to 15 percent of iron particles through 28 mesh, molding the mix into a brick and drying the brick.

10. The process of making an unfired basic refractory brick which is of increased strength at intermediate temperature, which comprises mixing from 45' to 70 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from 25 to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and chromite particles, and from 3 to 15 percent of iron particles through 28 mesh and a binder, molding the mix into a brick and drying the brick.

11. The process of making an unfired basic refractory brick which is of increased strength at intermediate temperature, which comprises mixing from 45 to '70 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from 25 to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and chromite particles, from 3 to 15 percent of iron particles through 28 mesh and from 0.5 to 3 percent of sulphuric acid on the total of the dry refractory components, molding the mix into brick and drying the brick.

12. The process of making an unfired basic refractory brick which is of increased strength at intermediate temperature, which comprises mixing from 45 to '70 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from 25 to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and chromite particles, from 3 to 15 percent of iron particles through 28 mesh, and from 0.5 to 3 percent of magnesium sulphate on the total of the dry refractory components, with water, molding the mix into brick and drying the brick.

13. The process of making an unfired basic refractory brick which is of increased strength at intermediate temperature, which comprises mixing from 45 to '70 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from 25 to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and a mixture of magnesia particles and chromite particles to the extent of not more than 10 percent of the brick, from 3 to 15 percent of iron particles through 28 mesh, and a binder,

9 molding the mix into brick, curing the brick with carbon dioxide and drying the brick.

14. The process of making an unfired basic refractory brick which is of increased strength at intermediate temperature, which comprises mixing from 45 to '70 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from 25 to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and a mixture of magnesia particles and chromite particles to the extent of not more than 10 percent of the brick, from 3 to percent of iron particles through 28 mesh, and from 0.5 to, 3 percent of sulphuric acid on the total of the dry refractory components, molding the mix into brick, curing the brick with carbon dioxide and drying the brick.

15. The process of making an unfired basic refractory brick which is of increased strength at intermediate temperature, which comprises mixing from 45 to 70 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and a mixture of magnesia particles and chromite particles to the extent of not more than 10 percent of the brick, from 3 to 15 percent of iron particles through 28 mesh, and from 0.5 to 3 percent of magnesium sulphate on the total of the dry refractory components, with water, molding the mix into brick, curing the brick with carbon dioxide and drying the brick.

16. The process of making an unfired basic refractory brick of increased strength at intermediate temperature, which comprises mixing from 45 to '10 percent of coarser refractory particles of the class consisting of magnesia particles between 6 and mesh and chromite particles between 6 and 28 mesh, from 25 to 50 percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and a mixture of magnesia particles and chromite particles to the extent of not more than 10 percent of the brick, and from 0.5 to 3 percent of sulphuric acid, subsequently mixing from 3 to 15 percent of iron particles through 28 mesh with the other ingredients, molding the mix into a brick and drying the brick. i 17. The process of making an unfired basic refractory brick of increased strength at intermediate temperature, which comprises mixing from to '70 percent of coarser refractory partic-les of the class consisting of magnesia particles between 6 and 35 mesh and chromite particles between 6 and 28 mesh, from 25 to percent of finer refractory particles through 48 mesh of the class consisting of magnesia particles and a mixture of magnesia particles and chromite particles to the extent of not more than 10 percent of the brick, and from 0.5 to 3 percent of sulphuric acid on the total weight of the dry refractory components, and from 2 to 5 percent of water on the weight of the dry refractory components, subsequently incorporating from 3 to 15 percent of iron particles through 28 mesh in the mix, molding the mix into brick, curing the brick with carbon dioxide and drying the brick.

RUSSELL PEARCE HEUER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,715,449 Curtis June 4, 1929 2,283,250 Goldschmidt, et al. May 19. 1942 2,394,304 Griffith Feb. 5, 1946 FOREIGN PATENTS Number Country Date 119,101 Great Britain .-a,--.--- 1918 

1. A BASIC REFRACTORY BRICK, UNFIRED AND SUITABLE FOR USE IN UNFIRED CONDITION, COMPRISING FROM 45 TO 70 PERCENT OF COARSER REFRACTORY PARTICLES OF THE CLASS CONSISTING OF MAGNESIA PARTICLES BETWEEN 6 AND 35 MESH AND CHROMITE PARTICLES BETWEEN 6 AND 28 MESH, FROM 25 TO 50 PERCENT OF FINER REFRACTORY PARTICLES THROUGH 48 MESH OF THE CLASS CONSISTING OF MAGNESIA PARTICLES AND CHROMITE PARTICLES, AND FROM 3 TO 15 PERCENT OF IRON PARTICLES THROUGH 28 MESH. 